Transflective LCD Chromaticity Reduction via Patterned Quarter Wave Foil
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Solution Overview
Problem
Transflective liquid crystal displays face challenges in achieving high contrast, brightness, and low color shift over a wide range of viewing angles while being cost-effective and easy to manufacture, due to issues with circularly polarized light and the complexity of patterning quarter wave foils.
Innovation Solution
A 90°-twisted transflective cell with a patterned quarter wave foil (QWF) is used, where the optical axis of the QWF is oriented at 45° to the polarizers, and the LC director is rotated relative to the polarizers to reduce chromaticity, eliminating the need for additional half wave foils and simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a patterned quarter wave foil (QWF) is used to cover only reflective subpixels, then the transmissive portion can use linearly polarised light improving brightness and efficiency, but the QWF introduces chromaticity (color shift) that degrades display quality
Solution Approach 1:
A half-wave foil (HWF) is introduced as an intermediary optical element between the patterned QWF and the transmissive subpixels. The HWF converts the linearly polarized light from the transmissive portion into circularly polarized light, which then passes through the LC layer and is converted back to linear polarization by the QWF in the reflective portion, eliminating chromaticity while maintaining brightness
Solution Approach 2:
The patent changes the polarization state parameter of light by introducing the HWF, transforming linear polarization to circular polarization and back, which resolves the chromaticity issue introduced by the patterned QWF while maintaining the brightness benefits of using linearly polarized light in the transmissive portion
2Object-affected harmful factors
If an achromatic quarter wave foil (AQWF) is used to eliminate chromaticity, then color accuracy improves, but the transmissive portion efficiency decreases because twisted LC modes are less efficient at converting circularly polarized light
Solution Approach 1:
The display is segmented into transmissive and reflective subpixels with different optical paths. The transmissive subpixels use linearly polarized light for high efficiency, while the reflective subpixels use circularly polarized light through the patterned QWF + HWF combination for chromaticity elimination, allowing each portion to be optimized independently
Solution Approach 2:
Different regions of the display have different optical properties: the transmissive portion has linear polarization for brightness efficiency, while the reflective portion has circular polarization for chromaticity reduction. The patterned QWF and HWF create local quality differences that optimize each subpixel type for its specific function
3Object-affected harmful factors
If multiple films (patterned QWF and HWF) are used to achieve achromatic reflective mode, then chromaticity is reduced, but the number of films and manufacturing complexity increases
Solution Approach 1:
The patterned QWF and HWF are combined in a specific configuration where the HWF is placed between the QWF and the transmissive subpixels. This merging of optical elements creates a compact achromatic system that reduces chromaticity while minimizing the number of separate components compared to alternative approaches
4Device complexity
If a single patterned QWF is used without HWF to simplify manufacturing, then the number of films is reduced, but chromaticity increases and contrast is affected
Solution Approach 1:
The HWF serves as an intermediary element that bridges the single patterned QWF and the transmissive subpixels, enabling chromaticity reduction without requiring multiple separate films. The HWF mediates the optical path to achieve achromatic performance with minimal film count
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces chromaticity and maintains or improves brightness, allowing for a more efficient and cost-effective display with reduced manufacturing complexity, achieving high contrast and low color shift.
Implementation Method 1
at least one quarter wave retardation film (QWF) between the front polariser and the LC layer, which has an optical axis parallel to its film plane, comprises a pattern of regions with quarter wave (λ/4) retardation
Implementation Method 2
an LC layer sandwiched between a front and a back electrode, being switchable between different orientations upon application of an electric field and having a twist angle φ when no field is applied
Implementation Method 3
the reflective subpixel has a transmissive front electrode and a reflective back electrode
Data Source
AI summary
The invention relates to a transflective liquid crystal display (LCD) comprising a patterned quarter wave foil (QWF) and having improved chromaticity.